The present invention generally relates to bias voltage supplying circuits, and more particularly to a bias voltage supplying circuit which supplies a bias voltage for making an internal circuit of a semiconductor integrated circuit active.
Recently, various portable electronic equipments using storage cells have been developed. In such an electronic equipment, it is highly desirable that the power consumption is small so that the electronic equipment can be used for a long time with the limited power supply. On the other hand, in a semiconductor integrated circuit used in such an electronic equipment, a bias voltage supplying circuit is provided to supply a bias voltage to an internal circuit of the semiconductor integrated circuit. This bias voltage supplying circuit is activated by an independent activation circuit. In order to minimize the power consumption, it is necessary to suppress the power consumption of the activation circuit to the limit after the bias voltage supplying circuit is activated.
A conventional bias voltage supplying circuit which is provided with an independent activation circuit will now be described in conjunction with FIG. 1. FIG. 1 shows a bias voltage supplying circuit 1 and an internal circuit 2 which receives a bias voltage from the bias voltage supplying circuit 1. In1 through In4 denote input terminals for receiving input signals, and Ou1 denotes an output terminal. The internal circuit 2 is not directly related to the problems of the bias voltage supplying circuit 1, and a description of the circuit structure and operation with regard to the internal circuit 2 will be omitted.
A power source voltage Vcc from a battery power source, for example, is applied to the bias voltage supplying circuit 1. This power source voltage Vcc is applied to bases of transistors Tr1 and Tr2 via a resistor R1 and a diode D1. Hence, the transistors Tr1 and Tr2 turn ON, thereby turning ON transistors Tr3 and Tr4. The base potential of the transistors Tr3 and Tr4 is supplied to an output terminal 3 via transistors Tr7 and Tr8, and the voltage from the output terminal 3 is supplied to the internal circuit 2 as a bias voltage. Accordingly, the resistor R1 and the diode D1 form an activation circuit 4 which activates the bias voltage supplying circuit 1.
On the other hand, when the transistors Tr3 and Tr4 turn ON, the base potential of the transistors Tr3 and Tr4 is also applied to a base of a transistor Tr5. As a result, the transistor Tr5 turns ON, thereby turning ON a transistor Tr6. In this state, the anode potential of the diode D1 becomes lower than its cathode potential and a forward current of the diode D1 is cut off. Hence, the transistors Tr5, Tr6 and Tr9 form a stop circuit 5 for stopping the operation of the activation circuit 4. After the bias voltage supplying circuit 1 is activated by the activation circuit 4, the stop circuit 5 stops the operation of the activation circuit 5 so as to remove the undesirable effects of the activation circuit 4 on the bias voltage supplying circuit 1 and to prevent unnecessary power consumption caused by an unwanted current flowing through the activation circuit 4.
However, in the bias voltage supplying circuit 1 show in FIG. 1 a collector current continues to flow through the transistors Tr5 and Tr6 of the stop circuit 5 even after the current flowing through the diode D1 via the resistor R1 is cut off by the operation of the stop circuit 5. For this reason, a power consumption occurs at a part which is not directly related to the supplying of the bias voltage, and there is a problem in that the measures taken to reduce the power consumption of the bias voltage supplying circuit 1 is still insufficient. Therefore, there is a demand for an improved bias voltage supplying circuit which has an even smaller power consumption.